If you're looking for an all-natural way to lower your cholesterol -- in addition to watching what you eat and exercising -- there are plenty of dietary supplements on the market that claim to do the trick. Each year seems to bring a new alternative remedy -- garlic, ginseng, or red yeast rice, for example -- that users tout as the next best thing to get cholesterol under control.

There are plenty of dietary supplements that claim to lower cholesterol, but few have science behind them.

But just because your Uncle Jack says a supplement worked miracles on his cholesterol doesn't mean it will work for you. In fact, his success may be due to a placebo effect or a diet overhaul he neglected to mention.

• What it is: The dried extract of the artichoke leaf is also known as Cynara scolymus.

• The evidence: In 2000, German researchers performed a randomized, double-blind, placebo-controlled trial using nearly 150 adults with total cholesterol over 280 -- well into what the American Heart Association considers "high risk" territory. The participants who took an artichoke supplement for six weeks saw their levels of low-density lipoprotein (LDL), or bad cholesterol, fall by 23 percent, on average, compared to just 6 percent in the placebo group. Health.com: 7 causes of high cholesterol

These are promising numbers, but they haven't been replicated. A more recent, three-month trial of similar design found that total cholesterol fell by an average of 4 percent among participants taking artichoke leaf extract, but the researchers found no measurable impact on either LDL or high-density lipoprotein (HDL), also known as good cholesterol. They suggested that differences in the health of the participants and the potency of the supplements -- the patients in the second study received a dose about 30 percent smaller -- could explain the discrepancy between the results of the two studies.

• The bottom line: There have been very few quality studies conducted on artichoke leaf extract, and the mixed results suggest that more evidence is needed to confirm its effect on cholesterol. Don't expect your LDL to plummet if you take artichoke supplements.

Fenugreek

• What it is: Fenugreek is a seed (often ground into a powder) that has been used since the days of ancient Egypt and is available in capsule form.

Don't Miss

• The evidence: Several studies from the 1990s have reported that, in high doses, various fenugreek seed preparations can lower total cholesterol and LDL, in some cases dramatically. (One study recorded an LDL drop of 38 percent.) Almost without exception, however, the studies have been small and of poor quality, which casts some doubt on the validity of the results.

Fenugreek contains a significant amount of dietary fiber (anywhere from 20 to 50 percent, analyses have shown), and some experts speculate that the purported cholesterol-lowering effect of fenugreek may in fact be attributed largely to its fiber content. Health.com: Dietary Fats Can Help -- or Harm -- Your Heart

• The bottom line: Despite the studies frequently cited as proof of fenugreek's ability to lower cholesterol, there is not enough evidence to support its use.

Fiber

• What it is: Soluble fiber is a type of dietary fiber found in oats, barley, bran, peas, and citrus fruits, as well as in dietary supplements. (Though it is good for the heart in other ways, insoluble fiber does not affect blood cholesterol.)

• The evidence: In 1999, a team of Harvard Medical School researchers conducted a meta-analysis of nearly 70 clinical trials that examined the effect of soluble fiber on cholesterol levels. High soluble fiber intake was associated with reductions in both LDL and total cholesterol in 60 to 70 percent of the studies they examined. For each gram of soluble fiber that the participants of the various studies added to their daily diet, their LDL levels fell by about 2 points. (The average time frame was seven weeks.)

The amount of fiber you'd need to eat to significantly lower your LDL is a bit unwieldy. Most people eat far less than the 25 grams of dietary fiber recommended as a minimum by most health organizations -- and only about 20 percent of your total fiber intake is likely to be soluble. (Eating three bowls of oatmeal a day will only yield about 3 grams of soluble fiber, according to the Harvard researchers.) Taking daily fiber supplements can help, but they can cause some gastrointestinal side effects if taken regularly and can interfere with some prescription medications.

• The bottom line: A diet high in soluble fiber can lower your LDL. The effect is likely to be relatively modest, however, and loading up on soluble fiber may be impractical. Health.com: 10 best foods for your heart

Fish oil

• What it is: Fish is rich in two heart-healthy omega-3 fatty acids, EPA and DPA. In concentrated form, these fatty acids are the main ingredients in fish oil supplements, which are usually sold as gel capsules.

• The evidence: In clinical trials using relatively high doses (3 grams or more), fish oil has been shown to lower triglyceride levels -- the third component of your total cholesterol number -- by around 10 to 30 percent. (The higher your triglyceride levels, the more effective it is.) Fish oil doesn't lower LDL, however. The supplements actually tend to cause a slight rise in LDL, although the form this additional LDL takes is thought to be less damaging to the arteries.

High triglyceride levels have been associated with an increased risk of coronary heart disease, but lowering them is not as important as lowering LDL. In fact, some experts believe that triglycerides are a sign, rather than a cause, of heart disease risk. Health.com: Easy food swaps cut cholesterol, not taste

• The bottom line: Fish oil lowers triglycerides, especially in people with high triglycerides. The American Heart Association recommends that people who need to lower their triglycerides should, in consultation with their doctor, take 2 to 4 grams of fish oil a day; people with heart disease should consume about 1 gram a day of EPA and DPA (combined), preferably by eating fatty fish such as salmon.

Garlic

• What it is: Garlic is member of the onion family that is available as an oil, extract, or pill (in addition to its natural state).

• The evidence: In a 2000 report on garlic's impact on cardiovascular risk factors, the federal Agency for Healthcare Research and Quality found that garlic caused a small but measurable drop in both LDL and total cholesterol, but only in the short term (three months).

Subsequent research hasn't been encouraging, however. A high-quality 2007 study in the Archives of Internal Medicine compared raw garlic and commercial garlic supplements over a six-month period and found no measurable effects of the various garlic forms on total cholesterol, LDL, HDL, or triglyceride levels versus placebo. The following year, a meta-analysis that included only randomized, placebo-controlled trials also concluded that garlic has no effect on cholesterol.

• The bottom line: Though garlic may help lower LDL temporarily, its ability to meaningfully affect cholesterol levels is questionable at best.

Ginseng

• What it is: Ginseng is an herb native to Asia that has been used in traditional medicine for centuries and is now sold as capsules.

• The evidence: The research on ginseng and cholesterol is mixed but unconvincing. In a comprehensive 2005 review, a team of Harvard Medical School researchers noted that several studies had found a beneficial effect from ginseng on one or more cholesterol components. But most of the studies were small, only a few were randomized, and none were blinded or placebo-controlled. In one study, the researchers found a drop of 45 percent in LDL levels and a rise in HDL of 44 percent -- but it wasn't controlled, included only eight participants, and was funded by a Korean manufacturer of ginseng products.

• The bottom line: Though the results of the nonrandomized studies can't be ignored, there isn't enough to evidence to support the use of ginseng to lower cholesterol. Health.com: Good vs. bad cholesterol

Guggul

• What it is: A tree-resin extract, long used in Ayurvedic medicine, guggul contains plant sterols (guggulsterones) and is available in capsule form.

• The evidence: As with ginseng, the research on guggul and cholesterol is sketchy. Early studies reported reductions in total cholesterol, LDL, and triglycerides of 10 percent or more, but most of the studies were small and flawed. Then, in 2003, researchers at the University of Pennsylvania published a randomized controlled trial of more than 100 people with high cholesterol -- the first guggul study conducted in the U.S. -- in the Journal of the American Medical Association. They found that guggul had no measurable effect on total cholesterol, HDL, or triglycerides -- and that it caused an increase in LDL of about 5 percent. (LDL levels in the placebo group fell by roughly the same amount.)

• The bottom line: The 2003 JAMA study was a black eye for guggul. More research is needed, but for now there is not enough evidence to justify using guggul to lower cholesterol. Plus, some research has found that 20 percent of Ayurvedic medicines may be contaminated with lead or other toxins.

Niacin

• What it is: Niacin is a B vitamin (also known as nicotinic acid) that occurs naturally in meat, fish, and dairy. It's also available as a capsule.

• The evidence: Experts have known for decades that niacin helps lower cholesterol. Large trials -- most notably a six-year study of more than 1,100 people conducted in the 1970s -- have found that niacin can cause significant decreases in total cholesterol, LDL, and triglycerides. But its most notable effect is on HDL: Research shows that niacin can raise HDL levels by up to 35 percent. (In part, for this reason, niacin is commonly used in addition to statins, which lower LDL..)

The catch is that it only has this effect at high doses of 2 grams to 3 grams a day, a dose that is typically taken as an extended-release prescription drug (such as Niaspan). Niacin is available as an over-the-counter supplement in extended-release doses of 500 milligrams or more, but consistently taking large amounts of niacin can result in side effects ranging from skin flushing to liver damage.

• The bottom line: Niacin boosts HDL, but you shouldn't take it without consulting a doctor. The AHA warns that niacin supplements should not be taken in lieu of a prescription, due to the potentially serious side effects.

Red yeast rice

• What it is: Red yeast rice is a fungus that grows on rice and contains small amounts of a naturally occurring form of lovastatin, a type of statin that is also found in prescription medications.

• The evidence: Compared to that of most dietary supplements, the evidence of red yeast rice's efficacy is quite strong -- which isn't entirely surprising, given that red yeast rice is, in effect, a low-dose statin. In studies over the years (including in several high-quality trials), various red yeast rice preparations have been shown to lower LDL by around 20 to 30 percent, comparable to a prescription statin.

More recent studies have backed up these results. In the most recent trial, a 2009 study of patients who had stopped taking statins due to muscle pain, red yeast rice capsules lowered total cholesterol and LDL by 15 percent and 21 percent, respectively (compared to 5 percent and 9 percent for placebo).

• The bottom line: Red yeast rice is a potentially effective way to lower cholesterol, but its potency makes some experts wary -- and suspicious. The amount of lovastatin in red yeast rice pills varies widely across brands -- so much so that some brands appear to be spiked with lovastatin, according to an analysis performed by a consumer watchdog group. Inadvertently ingesting too much of a statin can cause side effects (such as muscle pain), and due to the safety concerns, experts discourage using off-the-shelf red yeast rice.

Health Library

• What it is: Soy protein is found in soy foods such as tofu, edamame, and soy milk. It is also sold as a powder in nutrition stores.

• The evidence: Ten years ago, the U.S. Food and Drug Administration began to allow labels on certain foods that contained soy; the labels said soy protein was low in saturated fat and dietary cholesterol, and it could help reduce the risk of heart disease by lowering LDL.

Soy consumption in the U.S. exploded, but since then, research has found that the effect of soy protein on LDL is relatively modest. A 2006 review by the American Heart Association's nutrition committee found that an average consumption of 50 grams of soy protein a day -- twice as much as the FDA says is necessary to reduce the risk of heart disease -- resulted in an average drop in LDL of just 3 percent. Nor did soy intake cause HDL levels to rise significantly.

• The bottom line: Soy protein does lower LDL, but only slightly. The size of the effect seems to have been overstated.